Hydrocracking for lpg production

ABSTRACT

Liquefied petroleum gas, herein referred to as &#39;&#39;&#39;&#39;LPG,&#39;&#39;&#39;&#39; is produced from heavy hydrocarbon distillates through the utilization of a two-stage hydrocracking process. The product effluent from the first stage is separated to provide a vaporous gasoline boiling range fraction which is utilized as the charge stock to the second stage.

United States Patent [191 Watkins 1 Feb. 27, 1973 HYDROCRACKING FOR LPG PRODUCTION [75] Inventor: Charles 11. Watkins, Des Plaines, 111.

[73] Assignee: Universal Oil Products Company,

Des Plains, 111.

[22] Filedi July 12, 1971 [21] Appl. No.: 161,586

[52] U.S. Cl. ..208/59, 208/58, 208/89,

208/103, 208/111 [51] Int. Cl. ....Cl0g 13/02, Clog 31/14, Clog 37/04 [58] Field of Search ..208/59 [56] References Cited UNITED STATES PATENTS 3,047,490 7/1962 Myers ..208/59 0/ urge Sfqck 3 3,215,617 11/1965 Burch et a1. ..208/59 3,256,178 6/1966 Haas et a1. ....208/89 3,516,925 6/1970 Lawrence et al. ..208/1 1 1 3,607,723 9/1971 Peck et a1 ..208/59 3,617,483 11/1971 Child et a1 ..208/59 Primary Examiner-Delbert E. Gantz Assistant Examiner-G. E. Schmitkons Attorney-James R. Hoatson, Jr. et a1.

[5 7] ABSTRACT Liquefied petroleum gas, herein referred to as LPG, is produced from heavy hydrocarbon distillates through the utilization of a two-stage hydrocracking process. The product effluent from the first stage is separated to provide a vaporous gasoline boiling range fraction which is utilized as the charge stock to the second stage.

7 Claims, 1 Drawing Figure Separation Sysfem\ HYDROCRACKING FOR LPG PRODUCTION APPLICABILITY OF INVENTION The present invention involves a process for the conversion of heavy stocks into lower-boiling hydrocarbon products. More specifically, the inventive concept herein described is directed toward a two-stage hydrocracking process for the direct production of LPG from heavier-than-gasoline hydrocarbon fractions and/or distillates. The phrase gasoline boiling range hydrocarbons is intended to connote various hydrocarbon fractions having an end boiling point which may range from about 350F. to about 450F. To some extent, the precise boiling range for a naphtha fraction depends upon the particular locale in which the same is defined. It is not, therefore, intended to limit the present invention to a particular boiling range when reference is made to gasoline boiling range hydrocarbons. Heavier-thamgasoline charge stocks, contemplated for utilization in the present combination process, will have, therefore, an initial boiling point in the range of about 350F. to about 800F. Thus, suitable charge stocks include kerosene fractions, light gas oils boiling up to a temperature of about 700F., heavy vacuum or atmospheric gas oils boiling up to a temperature of about 1,050F. and either intermediate, or overlapping fractions and mixtures thereof. Charge stocks, containing hydrocarbons which normally boil above a temperature of l,050F. (considered in the art as black oils) are suitable but will generally require a special form of pretreatment for the purpose of convetting the 1,050F.-plus material into lower-boiling hydrocarbons as well as eliminating metallic and asphaltenic contaminants.

The process of the present invention is probably most applicable in those areas which (1) have no virgin source of natural gas and (2) are remote from pipelines transporting the same. Furthermore, within the petroleum industry, it is generally conceded that the demand for natural gas is rapidly exceeding the supply thereof at a rate such that the latter will be exhausted in a period of about 7 to about 10 years. In many areas, LPG serves as a substitute for natural gas primarily for cooking and heating. A much preferred use for LPG is acknowledged to be as charge stock in a steam-reforming process for the production of a methane-rich synthetic natural gas, which is often referred to as town'gas."

OBJECTS AND EMBODIMENTS One object of the present invention is to convert heavy hydrocarbonaceous charge stocks to lower-boiling hydrocarbon products. A corollary objective is to produce maximum quantities of a propane/butane concentrate (LPG) from charge stocks boiling above the gasoline boiling range.

Another object of my invention is to afford a simplified, multi-stage process for the production of LPG from charge stocks boiling above the normal gasoline boiling range.

Therefore, in one embodiment, my invention is directed toward a process for the production of liquefied petroleum gas, which process comprises the steps of: (a) reacting a hydrocarbonaceous charge stock, boiling above the gasoline boiling range, and hydrogen in a first reaction zone, at hydrocracking conditions selected to produce gasoline boiling range hydrocarbons; (b) separating the resulting first reaction zone effluent in a first separation zone, at substantially the same pressure and at a temperature to provide a first vaporous phase containing gasoline boiling range hydrocarbons, and a first liquid phase containing hydrocarbons boiling above the gasoline boiling range; (0) reacting said first vaporous phase, in a second reaction zone, at hydrocracking conditions selected to convert normally liquid hydrocarbons to liquefied petroleum gas components; (d) separating the resulting second reaction zone effluent, in a second separation zone, at substantially the same pressure and a temperature in the range of about 60 to about F. to provide a second vaporous phase and a second liquid phase; and, (e) further separating said second liquid phase to provide a third liquid phase containing unreacted gasoline boiling range hydrocarbons and to recover said liquefied petroleum gas.

Other embodiments of my invention involve preferred processing conditions and techniques as well as catalytic composites for utilization within the hydrocracking reaction zones. In one such other embodirnent at least a portion of said third liquid phase is recycled to said second reaction zone.

SUMMARY OF INVENTION It is well known that LPG can be produced in relatively high yields from naphthas, or gasoline boiling range hydrocarbons, having end boiling points in the range of about 350F. to about 450F. In most commercial LPG installations, the general practice is to produce a naphtha charge stock with and end boiling point of about 380F. to about 410F. With charge stocks containing extremely heavy components e.g., those having normal boiling points in the range of 900F. to about l,050F. a relatively high severity operation is required to maximize the yields of the LPG propane/butane concentrate. The high severity operation, required to convert such heavy components directly to LPG, produces an adverse effect upon the stability of the catalytic composite employed in the reaction zone. A common practice involves the initial conversion of such heavy hydrocarbonaceous material into a 400F. end point naphtha through the use of a multiple-stage system, with a naphtha product subsequently being processed in a separate reaction zone for conversion into LPG.

As hereinbefore stated, the present invention involves a multiple-stage hydrocracking system for the direct production of liquefied petroleum gas from hydrocarbon charge stocks boiling above the normal gasoline boiling range. These heavy charge stocks, for example, a full boiling range gas oil having an initial boiling point of about 500F. and an end boiling point of about 1,050F., are generally contaminated through the inclusion of sulfurous and nitrogenous compounds. These charge stocks will, therefore, generally be subjected to a hydrotreating, or hydrorefining technique whereby the deleterious contaminating influences are converted into hydrogen sulfide, ammonia and hydrocarbons. I-Iydrorefining, or desulfurization reactions are effected at a maximum catalyst bed temperature of about 600F. to about 850F. a pressure in the range of about 500 to about 5,000 psig., a hydrogen concentration from about 1,000 to about 20,000 scf./Bbl. and a liquid hourly space velocity of from about 0.25 to about 10.0. Suitable desulfurization catalysts are thoroughly described in the literature, and only brief reference thereto is necessary therein. Suitable catalytic composites generally comprise a siliceous refractory inorganic oxide carrier material and at least one metallic component selected from the metals and compounds of the metals of Groups VHS and VIII of the Periodic Table. One commonly employed carrier material is a composite of alumina and from about 10.0 to about 90.0 percent by weight of silica. Suitable metallic components include chromium, molybdenum, tungsten, iron, cobalt and nickel. The Group VI-B metal, such as molybdenum, is usually present within the range of about 4.0 through about 30.0 percent by weight. The Group VIII metals, such as nickel, is present in an amount in the range of about 0.01 to about 10.0 percent by weight. In those instances where the catalytic composite is to contain a Group VIII noble metal, the same is generally present in an amount within the range of about 0.01 to about 2.0 percent by weight.

With respect to the hydrocracking reaction zones, maximum catalyst bed temperatures will be within the range of about 650F. to about 950F. and preferably from about 700F. to about 900F. In most applications of the present invention, the maximum catalyst bed temperature within the second hydrocracking reaction zone will be higher than that in the first hydrocracking reaction zone. The hydrocracking reaction zones are maintained under an imposed pressure in the range of about 1,000 to about 5,000 psig., and preferably from about 1,000 to about 2,500 psig. The rate of hydrocarbon charge will be in the range of about 0.25 to about 5.0 liquid hourly space velocity, and the hydrogen concentration will be in an amount of about 3,000 to about 30,000 scf/Bbl. The hydrocracking catalytic composites will comprise at least one metallic component selected from groups VI-B and VIII of the Periodic Table, rhenium, tin and germanium, and a composite and from about 12.0 to about 30.0 percent by weight of alumina. A particularly preferred catalytic composite for utilization in the second hydrocracking reaction zone wherein the greater proportion of LPG is produced, is one where the metallic components are impregnated or ion-exchanged upon a crystalline aluminosilicate molecular sieve, a variety of which are commonly referred to in the art by the broad term zeolites. For example, one such catalyst which exhibits the desired characteristics of stability and activity, is a composite of about 5.3 percent by weight of nickel and a synthetically prepared faujasite which is distributed throughout a silica matrix. Other suitable zeolitic materials include mordenite, Type X or Type Y molecular sieves, as well as zeolitic material which is dispersed within an amorphous matrix of alumina, silica, or alumina-silica.

In view of the fact that hydrocracking reactions are principally exothermic in nature an increasing temperature gradient will be experienced as the charge stock and hydrogen traverse the catalyst. Therefore, in order to prevent too great a temperature rise in the hydrocracking reaction zones, it is contemplated that a quench. stream, either normally liquid, or normally gaseous, may be introduced at one or more points in the hydrocracking reaction zone. The fresh feed charge stock, in admixture with hydrogen and a 400F.-plus normally liquid recycle stream, is introduced into the first hydrocracking reaction zone at a temperature such that the increasing temperature gradient is maintained at the desired, predetermined level. The total product effluent is introduced, at substantially the same pressure, into a hot separator from which the gasoline boiling range hydrocarbons are removed as a vaporous phase. Prior to entering the hot separator, the temperature of the first zone effluent is decreased, via heatexchange to a level such that the vaporous fraction will contain a minimum of material boiling above the gasoline boiling range. The unconverted portion of the fresh feed charge stock is withdrawn from the hot separator as the liquid phase, and recycled to combine with the fresh feed charge stock. The vaporous phase serves as the charge to the second hydrocracking reaction zone, wherein the same is subjected to conversion to liquefied petroleum gas. It is within the scope of the present invention to divert a portion of the effluent from the first hydrocracking reaction zone to a suitable separation system. This affords a measure of flexibility in that it permits recovery of gasoline boiling range material when fluctuations in marketing considerations so demand. The pressure imposed on the second hydrocracking reaction zone is substantially the same as that at which the vaporous phase is withdrawn from the hot separator; however, the temperature will be increased to provide a higher severity operation. Again without a reduction in pressure, excepting that experienced from friction losses resulting from the flow of fluids through the system, the effluent from the second hydrocracking reaction zone is cooled to a temperature in the range of about 60F. to about F. and introduced into a cold separator.

A hydrogen-rich vaporous phase is withdrawn from the cold separator and recycled, by compressive means to combine with the fresh feed charge stock to the first hydrocracking zone. Make-up hydrogen, required to supplant that consumed within the overall process and lost via solution, is preferably introduced into the hydrogen recycle line downstream of the compressive means. Pressure control over the entire system is facilitated by monitoring the pressure of the vaporous phase as it emanates from the cold separator. A normally liquid phase, containing unreacted gasoline boiling range hydrocarbons, pentanes, hexanes, and the desired propane/butane concentrate is withdrawn from the cold separator and introduced into a suitable separation system wherein the various streams are recovered. The unreacted gasoline boiling range hydrocarbons are, at least in part, preferably recycled to combine with the material being charged to the second reaction zone. In one embodiment of my invention, a portion of the unreacted gasoline boiling range hydrocarbons is admixed with the effluent from the first reaction zone prior to introducing the same into the hot separator.

In further describing my invention, reference will be made to the accompanying drawing which illustrates one embodiment thereof. It is not intended that the invention be limited to the illustrated embodiment in which miscellaneous appurtenances such as heaters, pumps, compressors, heat-exchangers, start-up lines,

control valves, etc., have been eliminated. Such items are well within the purview of those possessing skill in the art, and are not essential to an understanding of my invention as hereinbefore described.

DESCRIPTION OF DRAWING The drawing will be described in conjunction with a commercially-scaled unit designed to produce maximum quantities of a propane/butane concentrate from a blend of relatively heavy gas oils. Pertinent properties of this fresh feed charge stock are presented in the following Table I:

TABLE 1: Gas Oil Charge Stock Properties The fresh feed charge stock is subjected to a hydrorefining technique utilizing a catalytic composite of an alumina-silica carrier material containing 37.0 percent by weight of silica, combined with 1.8 percent by weight of nickel and 16.0 percent by weight of molybdenum, calculated on an elemental basis. The reaction zone is maintained under an imposed pressure of about 2,000 psig., with a maximum catalyst bed tem' perature of about 850F. The fresh feed charge rate is 4,500 barrels per day, the hydrogen concentration is about 6,500 scf/Bbl. and the liquid hourly space velocity is 0.70. Hydrogen consumption, within the hydrorefining system is about 770 scf/Bbl. or 1.32 percent by weight of the total fresh feed. The hydrorefining yields and product distribution are presented in the following Table 11:

TABLE II: l-lydrorefining Product Distribution and It will be noted from the foregoing Table 11 that, although the principal reactions effected are desulfurization and denitrification, a significant quantity of hydrocracking is effected to produce lower-boiling hydrocarbons. The 111 BblJday or propane/butane concentrate will be added to the overall liquefied petroleum gas pool, while the heptane-390F. naphtha fraction, in an amount of 634 Bbl./day, will be introduced into the second hydrocracking reaction zone. The 4,035 barrels per day of 390F.-plus hydrocarbonaceous material constitutes the charge to the present two-stage process in line 1, as indicated on the accompanying drawing.

The charge in line 1 is admixed with about 2,400 barrels per day of a normally liquid recycle stream from line 2, the source of which is hereinafter set forth, resulting in a combined liquid feed ratio of about 1.6. Recycle hydrogen, in an amount of about 10,000 scfJBbl is admixed via line 3, the total charge continuing through line 1 into hydrocracking reactor 4. Reactor 4 is maintained under an imposed pressure of about 2,100 psig., with a maximum catalyst bed temperature of about 750F. The liquid hourly space velocity, based only upon the 4,035 barrels per day of fresh feed, is 0.81. The product effluent is withdrawn by way of line 5 and, following heat-exchange to reduce its temperature to a level of about 400F., is introduced into hot separator 6 at a pressure of about 2,075 psig. The product yield and distribution from hydrocracking reactor 4 is given in the following Table 111:

TABLE I11: Reactor 4 Product Distribution and Yields The yields presented in the foregoing Table III are exclusive of the 2,400 Bbliday of 390F.-plus material withdrawn from hot separator 6 as a normally liquid phase, and recycled via line 2 combined with the 4,035 Bbl./day of charge stock in line 1.

A principally vaporous phase is withdrawn from hot separator 6 by way of line 7, combined with unreacted naphtha in line 8 and the 634 BbL/day of naphtha from the hydrorefining system (not illustrated in the drawing), the mixture continuing through line 7 into the second hydrocracking reaction zone 9. The charge enters reaction zone 9 at a pressure of about 2,050 psig. the maximum catalyst bed temperature being about 900F. The liquid hourly space velocity is about 1.0, and the quantity of hydrogen is the same as in reactor 4, less that which was consumed by the reactions being effected therein.

The product effluent from reaction zone 9 is withdrawn by way of line 10 and introduced into cold separator 11 at a pressure of about 2,025 lbs. following heat-exchange and further cooling to reduce the temperature to a level of about F. A hydrogen-rich recycle gaseous phase is withdrawn through line 3 and admixed with the charge stock in line 1, while a principally liquid phase, containing the propane/butane concentrate is withdrawn by way of line 12 and introduced into separation system 13. Ethane and lighter components are indicated as being withdrawn through line 14, the propane/butane concentrate through line 15, the pentane/hexane concentrate through line 16 and about 1,700 Bbl./day of normally liquid material by way of line 8 for recycle to combine with the vaporous phase in line 7.

Hydrogen consumption in reactor 9 is 1,560 scf./Bbl. of the total heptane-390F. material being charged thereto. Since the combined liquid feed ratio is 1.5, the hydrogen consumption, based only on fresh heptane- 390F. feed, is about 937 scf./Bbl.

Total liquid yields are presented in the following Table IV:

TABLE IV: Total Product Yields, Bbl./day

Liquefied Petroleum Gas is produced in a total amount of 4,020 BbL /day, inclusive of the 111 BbL/day derived from the hydrorefining reaction zone, or 89.3 vol. percent of the original fresh feed of 4,500 Bbl./day.

I c aim as my invention:

1. A process for the production of liquefied petroleum gas which comprises the steps of:

a. reacting a hydrocarbonaceous charge stock, boiling above the gasoline boiling range, and hydrogen in a first reaction zone, at hydrocracking conditions selected to produce gasoline boiling range hydrocarbons;

b. separating the resulting first reaction zone effluent in a first separation zone, at substantially the same pressure and at a temperature to provide a first vaporous phase containing gasoline boiling range hydrocarbons, and a first liquid phase containing hydrocarbons boiling above the gasoline boiling range;

c. reacting said first vaporous phase, in a second reaction zone, at hydrocracking conditions selected to convert normally liquid hydrocarbons to liquefied petroleum gas components;

d. separating the resulting second reaction zone effluent, in a second separation zone, at substantially the same pressure and a temperature in the range of 60F. to about F., to provide a second vaporous phase and a second liquid phase; and,

e. further separating said second liquid phase to provide a third liquid phase, containing unreacted gasoline boiling range hydrocarbons, and to recover said liquefied petroleum gas.

2. The process of claim 1 further characterized in that at least a portion of said first liquid phase is recycled to said first reaction zone.

3. The process of claim 1 further characterized in that at least a portion of said third liquid phase is recycled to said second reaction zone.

4. The process of claim 1 further characterized in that at least a portion of said third liquid phase is recycled to said first separation zone.

5. The process of claim 1 further characterized in that said first and second reaction zones are catalytic, and contain a catalytic composite of a porous carrier material and at least one metallic component selected from Groups Vl-B and VIII of the Periodic Table.

6. The process of claim 5 further characterized in that the catalyst disposed in said first reaction zone is a composite of an amorphous carrier material, a Group Vl-B metal component and an iron-group metal component.

7. The process of claim 5 further characterized in that the catalyst disposed in said second reaction zone is a composite of a zeolitic carrier material and a Group VIII metal component. 

2. The process of claim 1 further characterized in that at least a portion of said first liquid phase is recycled to said first reaction zone.
 3. The process of claim 1 further characterized in that at least a portion of said third liquid phase is recycled to said second reaction zone.
 4. The process of claim 1 further characterized in that at least a portion of said third liquid phase is recycled to said first separation zone.
 5. The process of claim 1 further characterized in that said first and second reaction zones are catalytic, and contain a catalytic composite of a porous carrier material and at least one metallic component selected from Groups VI-B and VIII of the Periodic Table.
 6. The process of claim 5 further characterized in that the catalyst disposed in said first reaction zone is a composite of an amorphous carrier material, a Group VI-B metal component and an iron-group metal component.
 7. The process of claim 5 further characterized in that the catalyst disposed in said second reaction zone is a composite of a zeolitic carrier material and a Group VIII metal component. 